3 large ears of yellow corn, husked
2 small zucchini, halved lengthwise
1 tablespoon vegetable oil
1 lime
1 medium avocado, finely diced
1 small tomato, cored and finely diced
2 tablespoons finely diced red onion
½ cup sour cream
½ teaspoon cumin
½ small jalapeño (leave in the seeds for spicy!), finely minced, plus more for seasoning
2 tablespoons chopped cilantro, plus more for garnish
3 tablespoons crumbled Cotija cheese
½ teaspoon kosher salt, plus more to taste
Freshly ground black pepper to taste
Grill the vegetables:
Preheat a grill or grill pan over high heat, then add the corn, turning every 2–3 minutes, until blackened in spots on each side, 10–12 minutes total. Remove to a plate to cool.
Brush the zucchini with the oil, season generously with salt and pepper, and grill, flipping once halfway through, for 10 minutes total. Remove to a plate to cool for 10 minutes. Chop the zucchini into small pieces.
To cut the corn off the cob, place a small bowl upside down inside a larger bowl. (This helps catch all the little corn pieces!) Stand each ear of grilled corn on the smaller bowl, and, using a sawing motion, cut off the corn from the cobs, getting as close to the cob for maximum corniness (but not so close that you cut off and include the woody parts of the cob itself). You should have about 2 cups.
Make the dip:
Zest the lime into a medium bowl, then juice half the lime into the bowl (you should have 1 tablespoon juice); reserve the other half for seasoning at the end.
Add the avocado and toss to coat. Add the grilled corn and zucchini, tomatoes, and onions. Gently stir in the sour cream, cumin, jalapeño, ½ teaspoon salt, and cilantro. Season with more lime juice and jalapeño, if desired.
Transfer to a bowl and garnish with Cotija cheese and more cilantro.
