Toss chicken with flour so it is lightly dusted. Heat 2 Tbsp oil in large nonstick skillet on high. When oil smokes, add chicken in one layer. Sprinkle with salt and pepper.
When chicken browns on one side, toss it and cook until just about done, 5 min for smaller pieces & 10 min for larger pieces.
Remove chicken to plate and allow pan to cool.
Add remaining oil to pan, heat, add garlic and cayenne pepper, cook, stirring, about 2 min. Add the ketchup and stir, cook until ketchup bubbles, then darkens slightly. Return chicken to pan and stir to coat with sauce. Adjust seasoning and serve.