In a mixing bowl combine tomatoes, green onion, cilantro, jalopeño, salt, black pepper, cumin and cheese; mix well.
Drizzle a little oil to coat a skillet and heat over med-low heat. Place a piece of tortilla on a skillet and spread about 3 tablespoonfuls of tomato-cheese mixture onto a half side of the tortilla. Fold over the other half side and press gently with spatula to sear. Cook until golden brown, about 2-3 minutes. Flip to the other side and continue to cook for another 1-2 minutes adding a little more oil to the skillet if needed
Cut the quesadillas into wedges and serve warm with sour cream.