In fry pan over medium-high heat, warm 1 tsp oil. Cook pancetta until crispy. Add garlic; cook 30 seconds. Drain on paper towels. Transfer pancetta mixture to small bowl; stir in sage.
Create pocket in each chicken breast by laying breast on a work surface with the pointed end away from you. Insert long paring knife in the center of the end closest to you (rounded end). Move the knife around to enlarge the opening; forming a pocket.
Season chicken on both sides with salt and pepper. Stuff each breast with 2 tbsp cheese and 1 tbsp pancetta mixture. Set chicken on wire rack-lined baking sheet. Freeze for 5 minutes.
Put flour, egg whites and bread crumbs in separate breading pans. Dredge chicken in flour, then dip into egg whites anc coat evenly with bread crumbs, pressing so they adhere. Set chicken on wire rack-lined baking sheet; refrigerate 15 minutes.
In wide pan over high heat, heat 1 1/2 cups oil. Fry chicken in batches, 5-6 minutes. Turn chicken; reduce heat to medium. Cook until chicken is coated through, 7-8 minutes; add more oil if needed. Drain on paper towels.