Pack the red onions and jalapeños in a jar or glass dish. Mix the lime juice, honey, and salt in a measuring cup and pour over the onions and jalapeños. Cover and refrigerate for at least 1 hour (can be made up to 3 days ahead).
Prepare a hot grill. Rub the ears of corn with olive oil, sprinkle with salt and pepper, and grill, turning occasionally, until they’re bright gold with a little bit of char. Allow them to cool, then slice the kernels from the cob.
Toss the corn with tomatoes, avocados, and as many of the pickled red onions and jalapeños as you like, along with a few tablespoons of the pickling juice. Use up the rest on salads and tacos.
Top the salad with queso fresco and cilantro, and season with a bit more salt and pepper to taste