Cook onion in 2 tablespoons oil till tender but not brown.
Stir in undrained tomatoes, chili peppers, and oregano.
Simmer about 20 minutes till very thick.
In skillet dip each tortilla in 2 tablespoons hot oil about 10 seconds or just till limp.
Drain on paper toweling.
Cut cheese into 12 strips.
Place 1 strip of cheese and 2 tablespoons sauce down center of each tortilla; overlap edges.
Arrange on baking sheet, seam side up.
Bake, covered, in 350° oven for 8 minutes.
Uncover; bake 3 to 4 minutes more.
Open tortillas and add sour cream; roll up.