Preheat the oven to 425 degrees F. Line 2 sheet pans with parchment paper.
On one sheet pan, toss the corn with 1 tablespoon olive oil, 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper, spreading the kernels in a single layer. Roast the corn until it is crisp on the edges and lightly browned, about 20-25 minutes.
In a large bowl, stir the black beans, red onions and jalapeños with 1 tablespoon olive oil, cumin, garlic powder, paprika, oregano, 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper. Once they are coated in the spiced oil mixture, lightly mash the beans with a fork.
Stir the corn into the black beans.
Warm the tortillas, wrap them in a damp paper towel. Microwave for 30 seconds. This steams the tortillas, so then you can fold them to assemble the tacos.
On the other sheet pan, brush each tortilla with olive oil on both sides. Spoon the filling (about 1/3 cup not packed) onto one half of a tortilla. Then sprinkle the filling with cabbage and feta. Fold over the taco and gently press it down. Repeat for the remaining tortillas and filling.
Bake the tacos 5 minutes. Then flip them over. Bake for another 10 minutes. Flip them again and bake for 5 minutes until they are golden brown and crisp on the outside.
To make the avocado crema, combine the avocado, yogurt, lime juice, water, cilantro and pinches of salt and pepper in the bowl of a food processor. Puree until smooth. (You may need to add another tablespoon of water to thin it out.)
Arrange the tacos on a serving plate. Top with chopped cilantro and serve with avocado crema on the side or drizzled over the tacos.