For the Salsa: In a medium bowl, toss together radishes, fennel (plus fronds, if using), scallions, cilantro, jalapeño, and lime juice. Season with salt and pepper to taste.

For the Quesadillas: In a large cast iron skillet or on the flat side of a cast iron griddle, heat 1/2 tablespoon oil over medium-high heat until lightly smoking. Add chorizo and cook until browned, turning once, about 3 minutes. Remove from pan with a slotted spoon onto a paper towel–lined plate.

• Set out 4 tortillas on a work surface and sprinkle approximately 1 ounce (28g) cheese over half of each tortilla. Scatter chorizo and scallions on top of cheese, then top with remaining cheese. Fold tortillas in half over filling to form a half-moon shape.
• Add remaining 1/2 tablespoon oil to skillet or griddle and heat over medium-high heat until lightly smoking.
• Add quesadillas to skillet or griddle in a single layer, working in batches if necessary. Cook until lightly browned, about 4 minutes. Flip quesadillas and cook until second side is crisp and cheese is fully melted, about 3 minutes. Add more oil as needed if working in batches. While cooking any remaining batches, keep finished quesadillas warm by arranging them on a baking sheet in a single layer and holding them in a 250°F oven.
• Cut quesadillas into wedges and serve with radish and fennel salsa.