If using fresh corn, slice kernels from the cob; for extra flavor, char on a hot skillet 3–4 minutes and let cool.
Drain and rinse black beans thoroughly and set aside to remove excess water.
Seed and dice the tomatoes and add them to a large mixing bowl.
Finely dice red onion and jalapeño (remove seeds for milder heat) and add to the bowl.
Add the corn and black beans to the tomato mixture and toss gently to combine.
Add chopped cilantro, ground cumin, salt and pepper; toss again to distribute seasoning.
Squeeze lime juice and drizzle olive oil over the mixture; toss to coat everything evenly.
Gently fold in the diced avocado to keep pieces intact.
Taste and adjust seasoning — add more lime, salt, or a pinch of sugar if needed.
Let the salsa rest 10–15 minutes for flavors to meld, then serve with chips or as a topping.