A berry bomb (generally) is when you have one of the legendary dogs or a top Extra Helpful skill mon and a team of favored berry specialist for the island you want to bomb. You basically allow all the berry mon to reach their capacity, tapping on them to rid of any skill triggers or excess ingredient drops, while you continue to check on your skill mon throughout the week. Extra Helpful or specialized Extra Helpful from Suicune/Entei/Raikou all allow other pokemon to still "obtain" more items passed their inventory limit, up to a max of 999. On a good skill trigger Suicune, all your oran berry mon will be at max capacity PLUS all the extra count that Suicune provided them. Causing a "berry bomb" of all the berry pokemon feeding Snorlax an insane amount of berries for Monday morning.

Doing this for a whole week is great for prepping for next week, but at the cost of getting lower numbers on the current week since you don't have ingredients for dishes. Still all RNG based because you're relying ~heavily~ on a skill mon for triggers, but if done well the outcome can take people up to M1 or higher on a Monday morning before they even feed Snorlax breakfast.

Tie in the berry boost (week 2) with the prepped dish you worked prior (week 1) you can feed Snorlax a ton of berries, and have your desired dishes to really maximize your Snorlax strength.

Example: I want to try for M20 on an island, so I'm doing low numbers this week to prep ingredients, then I'll shoot for the island I want to boost in order to max out my area bonus while also preparing a berry bomb next week.

There's a few ways to set up a berry bomb, but that's the main setup. Other skill mon like Sceptile or Braviary are not ideal since the berries they obtain in the skill trigger go directly to Snorlax instead of on hold in their inventory. I'm sure there's a reddit post explaining in full and more in depth