Combine tomatoes, onion, cilantro, lime juice, and cumin in a large bowl.
Preheat an outdoor grill to medium heat and lightly oil the grate.
Coat corn and jalapeno peppers with olive oil.
Place corn and jalapenos on the preheated grill and cook, turning every 3 minutes, until corn is charred, about 15 minutes total. Transfer to a cutting board and let cool 5 minutes.
Dice jalapenos and cut corn kernels from the cob. Add jalapenos and corn kernels to the bowl of tomato-onion mixture; stir until well combined. Season with salt and pepper.