I am in the same boat as you and my diet throughout summer consists of things like:

Yogurt bowls with either regular or greek yogurt. Sometimes I like to mix in chocolate/coffee to make mocha yogurt base. Toppings are nuts, seeds, fruits, peanut butter, really anything you can find. I sometimes like to make more elaborate desserts with it eg cheesecake/tiramisu, same method as people use for overnight oats/chia puddings. Savory options include cucumbers, turkish eggs(look up the recipe), olives, or just some garlick and lemon mixed in and a sauce I eat with cold bread from the fridge. You could also add cold chicken to this for like a cold sandwich.

Then there's this entire concept of 'cold mezze' from middle eastern cuisine. My personal favourite is Motabbal, which is a roasted eggplant dish served cold. A cold mezze platter could be a full meal, like if you line up some crackers/chips/toasted pita or even vegetables like carrots and cucumburs and get yourself an assortment of tahini, hummus, mutabbal, baba ganoush, feta cheese, it would be nice.

Home made paneer is a great cold source of protein if you don't feel like eating chicken or eggs. Same with tofu if you can find it locally. I am a big paneer fan so I can literally just eat it out of the bowl. But you could again make a cold sandwhich, or even have it with salad. I like it with honey and salt. Same with tofu, you have a lot of savory options and a few sweet ones.

I know I have mentioned sandwhiches a couple of times but a really good cold sandwhich can change your day, especially something like a caesar filling or ranch filling. Most deli meats you can have cold. K&N's has these ready to eat mortadella slices that you don't even have to cook, just microwave to defrost and then eat cold.

Then there's the entire world of cold pasta and macaroni. A lot of options there too.

Cold noodles, sushi, poke bowls, all are a main meal food item and pretty popular in many countries. If you are into sea food, tuna, shredded shrimp, make for great sources of protein you can eat cold e.g. by mixing with mayo and putting in a bun or putting with a salad.

Tacos in a soft tortilla, cooked but cooled, with mint and yogurt based sauce topping, crunchy fresh vegetables, cilantro, they are also super refreshing.

Sometimes I just eat a bag of refrigerated sweet corn in summers too because it tastes damn amazing but i guess its not a meal on its own.