This is the kind of dinner I spend the day fantasizing about (and it just so happens to be what I've always wished poolside snack shacks would serve): freckled tortillas filled with just as many sautéed greens as strings of melty cheese—because as much as I love a cheesy quesadilla, I don't love dodging spurts of grease.
Sauté the hearty greens of your choice (kale, mustard, dandelion, collards) with shallots, chile flakes, and jalapeños. Then warm your tortillas—I prefer the texture and flavor of corn, though flour tortillas are generally more pliable and, in most parts of the US, available in larger sizes—and sprinkle the cheese on top.
Neither feta nor cheddar is traditional, per se, but I like the mix of something crumbly and salty with something sharp and oozy. For a similar effect, you could use cotija and Monterey Jack, or queso fresco and queso Oaxaca, or—why the heck not—goat cheese and Gruyère. When the cheese starts to soften, spoon the greens on top, slap one side of the tortilla over the other, and cook, flipping once, until the tortilla is browning and the cheese is melted (if you're lucky, it'll pull apart in gossamer strands as soon as you bite in).
Heat 1 tablespoon of butter in a large skillet. When hot, add the shallot, jalapeño, chile flakes, and garlic. Once the shallot is starting to soften and color, 3 to 5 minutes, add the washed greens, with water still clinging to their leaves. Season with salt and cook until very tender, 10 to 15 minutes, then set aside.
Heat the remaining tablespoon oil or butter in a skillet until shimmering/melted. Tilt the pan to distribute evenly across the surface. Add as many tortillas as will comfortably fit and cook on one side until they have softened, 2 to 3 minutes. Distribute cheese over the tortilla, then add a few tablespoons of the cooked greens to one side. Fold the tortilla in half with a spatula to cover the greens.
Cook until the tortilla begins to brown on one side, 2 to 3 minutes, and then flip onto the other side and cook until the tortilla browns on that side and the cheese is melted, about 2 to 3 minutes more. Repeat until you've used all of the tortillas.
Keep warm in a 250° F until all of the quesadillas have been made. Serve with salsa, lime wedges, and/or guacamole or avocado slices.