In a shallow bowl, toss the chicken in the flour to coat it well.
Put about half of the oil into a large skillet set over medium-high heat. When the oil is hot, cook the chicken in batches (without crowding the pan), sprinkling with salt and pepper, turning as needed until browned and cooked through. Transfer to a plate and let the pan cool slightly.
Add the remaining oil to the pan and cook the garlic for a minute or two, then add about half a cup of water and the ketchup and Sriracha and stir, loosening any browned bits on the bottom of the pan.
Cook for a few minutes or until the sauce bubbles, thickens and darkens slightly.
Return the chicken to the pan and stir to coat with the sauce.
Cover for a few minutes to heat through and ensure the chicken is cooked through. Serve over rice.