I start by heating olive oil in a large skillet over medium-high heat. Once it's shimmering, I toss in the diced onion and bell peppers. I let them cook for about 6 to 8 minutes, stirring occasionally, until they're softened but still have a little bite left in them.
Next, I stir the cooked turkey, black beans, and taco seasoning right into the pan with the vegetables. I mix everything together for a minute or two so the seasoning coats every piece evenly. Then I pull the pan off the heat and transfer the filling into a bowl.
I wipe out the same skillet with a paper towel and set it back over medium heat. I lay a tortilla flat in the pan, sprinkle cheese over one half, spoon on a generous portion of the turkey filling, then top it with a little more cheese before folding the tortilla closed.
I let the folded tortilla cook for about 2 to 3 minutes per side, pressing down gently with my spatula so it browns evenly and the cheese melts all the way through. Once both sides are golden, I move it to a cutting board and repeat with the rest.
Finally, I cut each quesadilla into wedges using a pizza cutter so the cheese doesn't drag everywhere. I serve them hot, right off the pan, with sour cream and salsa on the side for dipping.