Pound chicken with a meat mallet to 1/2-in. thickness; sprinkle with salt and pepper. Lightly coat both sides with flour; shake off excess.
In a nonstick skillet, cook bacon over medium-high heat until crisp, stirring occasionally. With a slotted spoon, remove bacon to paper towels; reserve 1 teaspoon drippings.
In same pan, heat butter and drippings over medium heat. Add chicken; cook until no longer pink, 4-6 minutes per side. Remove from pan.
Add garlic, rosemary and pepper flakes to pan; cook and stir until garlic begins to color, 1-2 minutes. Stir in broth and lemon juice; bring to a boil, stirring to loosen browned bits from pan. Cook until slightly thickened, 3-4 minutes.
Return chicken and bacon to pan; heat through, turning chicken a few times to coat.