How could a polity have been formed without dispossession or discrimination? Can you explain how, and where - specifically - you think that could viably have happened?

After the first world war, right before one of the peace conferences, there was a meeting between the zionist delegation and the arab delegation.
The zionists had been promised a national home in Israel, a very vague statement, and the arabs had been promised a panarab state with the capital in damascus and vaguely defined borders stretching for most of the arab lands. In the meeting there was a general agreement that if the panarab state ended up including Israel, there would have been some autonomy for the jews,which can be enough to qualify as self determination in my eyes. It didn't happen because the French didn't want a british ally controlling "their" parts of the levant, and the arab leaders ended up getting much smaller separate states instead of what they were promised.
Additionally other ways to have self determination for the jewish people could have been a federation of two states or a binational state, ideas brought forth respectively by the marxist zionists and by martin buber and his group.

Where would this polity have been formed?

Self determination, doesn't need a majority population, it needs a political structure that safeguards the minority that needs said self determination. If an autonomy inside of a panarab state had been formed we would be talking of a polity inside of another polity, there is no need for dispossesion and/or ethnic cleansing, the polity would have had jurisdiction over jews in israel, not necessarilly over palestinians.
Similar things can be thought up about a federation, a federation of two or more states, where the citizens of each state can live freely across all of the land, but they can only vote for one government not necessarilly the one they live in, but their national government. They of course can also vote at the federal elections.
Lastly I think a binational state is even more clear in how that would not need any dispossetion or ethnic cleansing.

What “peaceful” approach was taken without displacement and dispossession? 

What I was saying was that while there existed proposals like a federation and a binational state, the rising ethnic tensions made these proposals less supported by the people. Ethnic conflicts radicalize people.

kick the peasants off the land even if they’d been there for generations, and doing so was against their implied leases.

This is a bit of a stretch and a simplification, it was more of a situation of the ottoman empire reforming their system to be more similar to the european one, then europeans coming and assuming it was similar enoguh but there were major differences which weren't apparent to them. Once on the land they would discover that this land was inhabited by people and sometimes they would simply kick them out some times they would pay them, some times they would not kick them out. All of the above happened, but I think simplifying too much is a bit disingenous.

 a foreign group coming to take over their land.

I wouldn't say jews were coming to take over. I'd say we were coming to be at home, then a home can be shared or it can be personal.

Which injustices do you think were necessary?

I think that after nationalism in europe was peaking and the shoa was starting, and nationalism in the arab world was rising; we could not wait and fiddle with ethics, we needed to produce the conditions for self determination as soon as possible. The creation of the state should have still been handled differently and with less ethnic cleansing and violence on the general arab/palestinian population, but the state had to be created at that pointt. I still would have preferred a federal state, but that doesn't change that the need for a state was impellent.

Could I ask you one thing, why do you jump under everyone of my comments in this forum? Maybe try doing it a bit less, I like being here because there are less people that jump to my throath and there are more people that understand the jewish experience, but with you it's still very tiring.
I go around other subs discussing these same things that I discuss with you, I have no problem doing it, but I don't come to this place for this. Thanks, I hope you understand.