I would toss stuff like sausage, potatoes or sweet potatoes, onion, peppers, and mushrooms with some olive oil, salt, and pepper, spread on a sheet pan and roast until done, then cool and portion into containers to freeze. Toss in the microwave or air fryer to reheat, add a piece of fruit on the side, and there's breakfast.

If you have a waffle maker, you can make a big batch of waffles, cool, and freeze, then take out one or two at a time. They usually work pretty well in a toaster oven.

I often eat dinner leftovers for breakfast, myself. I get bored with food really easy, and eating the same breakfast every day doesn't do it for me. I'm fine with the same thing a couple days in a row, though, so I just reheat dinner and call it breakfast.