Season onion and corn. Preheat an oven to 400F. Place sliced red onion and 2 cups of corn in an 8x8 baking dish. Drizzle with 2 Tbsp olive oil, then sprinkle with 3 tsp ground cumin and ½ tsp Kosher salt. Stir well.
Add feta and remaining ingredients. Wedge the 10 oz block of feta into the center of the baking dish, then add 3 sliced scallions, 2 thinly sliced jalapeños, ⅓ cup of cilantro leaves, and 1½ cups of shredded Cheddar cheese, ending with the cheese on top. Do not stir.
Bake. Transfer to a preheated oven and cook for 30 minutes, or until the feta is warm and melty.
Stir, then serve. Carefully use a spoon to stir everything together, making a smooth, cheesy dip. Garnish with additional scallions, jalepeño (if using), and cilantro. Serve immediately with some fresh lime juice squeezed on top, pita chips, crackers, or crostini. We recommend serving pickled jalapeños on top or on the side, depending on guests preferences.
