Salpicon or Machaca (as it's known up North where I am from) is a great choice for the hot weather and delicious!
You will need:
Carne para deshebrar or meat for shredding (can be skirt, flank, etc.)
oil (vegetable or olive)
salt and pepper
Tostadas (store bought or home made)
Easiest and fastest is to use a pressure cooker, otherwise you need a deep pot since this meat needs time to get tender. Put the meat into pot, cover with water and drop in: garlic, bay leaf, 1/2 onion (don't chop, just throw in). Bring to a boil and lower heat to simmer and cook until meat separates easily (maybe 1 hour or 2, keep checking), for pressure cooker: close the pressure cooker up and wait for the valve to let you know to lower heat, put 45 min timer after you put on simmer. Once the meat is ready, allow to cool. The cooking liquid can be used for flavoring or as a soup base or for rice so you might want to save it. If you do and put it in the fridge, once it's cool there might be a 1/2 inch of fat on top which you can leave to have a more substantial consome or take off if you want a lighter stock. I leave it for rice and take off for stock, up to you.
When the meat is cooled, shred it by hand. At this point, chop: tomato, onion, cilantro (you can add chile serrano or peas, carrots, potato, etc. if you want to). Now you can toss it all together, add vinegar and a little oil and you're set, but if you want a more Machaca dish, then put tomato sauce, some of the stock, salt & pepper, a little brown sugar and incorporate it. Once it tastes to your liking you can add the meat and veggies. Great for burritos, flautas, enchiladas, tostadas, sopes, stuffed avocados, etc. and can be served hot while the other is a cold dish....