Add 1 tablespoon of olive oil to a large nonstick skillet over medium heat. When hot, add the onion and cook, stirring occasionally, until it starts to soften, about 2 minutes. Add the corn, ¼ teaspoon salt, cumin, paprika and garlic and cook, stirring occasionally, until tender, 3 to 4 minutes. Transfer to a small bowl and set aside.
In a medium bowl, whisk together the eggs, milk, remaining ¼ teaspoon salt and pepper. Set the skillet back over medium heat. Add the remaining 1 tablespoon olive oil. When hot, add the egg mixture. Cook, stirring frequently, until scrambled, 3–4 minutes. Remove from the heat.
If the bowl of veggies has any excess juices, drain them off. Add the veggies back to the skillet with the scrambled eggs. Add black beans and mix to combine. Taste and season with additional salt and pepper if desired.
Place a tortilla on your work surface. Spoon about 1/10th of the egg mixture on half of a tortilla, leaving a small border around the edge. Top with 1/10th of the cheese and 1 tablespoon salsa. Fold the empty half of the tortilla over the top of the filling to form a semicircle. Repeat with the remaining tortillas.
Wipe out the skillet that you used for the eggs and set over medium-high heat. When hot, mist lightly with an oil mister or cooking spray. Place an assembled quesadilla in the pan and cook for about 5–6 minutes, until both sides are browned and the cheese is melted, flipping once halfway through. Repeat this process with the remaining quesadillas.
Cut into triangles. Serve with optional toppings if desired.
If you're making these ahead to freeze, cook the veggies and eggs as directed above, then let them cool to room temperature before proceeding. Assemble the same way as directed above but do not cook in the skillet. Instead, wrap each assembled quesadilla individually in plastic wrap, then, to prevent bending, place in a single layer on a baking sheet or another flat surface that will fit in your freezer. Transfer to the freezer, freeze until firm, then move the quesadillas to a freezer bag or airtight container for storing in your freezer.When ready to eat, remove the plastic wrap, then warm in the microwave for 2 to 3 minutes until heated through. Alternatively, let them thaw out overnight in the fridge and then, in the morning, cook in a skillet as directed above.