I have limited space for meal prep and I don't really like cooking elaborate meals in a trailer (or anywhere else really but especially in a trailer!)
We usually don't have electric so no crock pots or microwaves.
Lunch often doesn't have a formal meal as we are often out and about. That means more food that's easy to carry and somewhat robust. Think bagels instead of toast, fruit, cheese, granola bars.
I have a set of nonperishable supplies at hand usually: pasta and a jar of sauce, 5 minute rice, ramen, various soups, beans, diced tomatoes, corn, carrots/peas, coconut milk. Spices. I haven't found a canned protein that I like, however I usually have some sort of precooked meat like the huge turkey breast hunks sold at costco. They don't expire as quickly as fresh meat and there is less worry about insufficient cooling.
Then it just depends what I have at home, and what I feel like making. By keeping nonperishable supplies in the trailer, I can fall back on a number of things like a beans curry, pasta with sauce, turkey casserole,
We usually carry salad kits. More expensive, but ideal for camping. Precut veggies are also great for stir frys and the like.
Not recommended are items with long cooking times, like boiling whole tomatoes. Also consider you have less heat available so getting a pan really hot might be a challenge. (at least for me - I don't want to boil my meat)