Place a non-stick frying pan, large enough for one tortilla to lie flat, over medium high heat. Add bacon and dry fry until crisp, turning once to cook on both sides. Remove from heat and drain on kitchen paper.
Add 20ml olive oil to the pan over medium heat. Add onions and cook, stirring frequently until soft and translucent. Remove to a bowl and wipe out pan with kitchen towel.
Brush one flour tortilla with extra olive oil. Place tortilla oil-side down into the clean pan. Taking care not to fill ingredients right to the edge, spoon or spread over the onions, then top with bacon, grated cheese, sprinkle on rocket leaves and season to taste.
Cover the second tortilla, pressing to seal. Brush top of the tortilla with remaining olive oil and place over medium high heat. Cook for 2-3 minutes, pressing down occasionally. Turn and cook for a further 2 minutes, until the cheese is slightly melted and the tortilla is crisp. Cut into wedges and serve immediately.
Note - To flip the quesadilla more easily, cover the top with a dinner plate and turn out the tortilla then slide back into the pan. This can also be cooked in a sandwich press.