Place orange zest and juice, lime zest and juice, beer, olive oil, garlic, jalapeno, cumin, salt, and pepper in the container of your blender. Blend for 10-15 seconds until smooth.

Pat beef dry and place in a bowl or food storage bag. Pour the marinade over the beef and massage it in using your hands. Place in the fridge to marinate for 1 hour.

Preheat your barbecue on high heat. Grill the whole jalapenos and the beef for 2-5 minutes per side until strong grill marks have formed and the beef is cooked to your liking (ideally medium-rare).

Place the beef on a wire rack to rest for 5 minutes. Thinly slice the beef against the grain, and the jalapenos into rings, then set aside for assembly.

Sprinkle one half of a tortilla with cheese, the arrange beef slices on top, followed by onion, jalapeno, and cilantro. Sprinkle with additional cheese, then fold over the empty half and give it a good press to hold it in place.

Heat a cast iron skillet on medium and drizzle it lightly with olive oil. Lay 1-2 quesadillas in the pan and cook for 2-4 minutes per side, flipping once the tortilla is golden brown and crisp, and the cheese is melted. Cool on a wire rack and slice before serving.