In a shallow bowl, combine flour, salt, pepper, garlic powder, and paprika. Stir with a fork or small whisk to blend evenly.
Dredge each chicken breast in the seasoned flour mixture until fully coated, shaking off the excess. Set aside on a plate.
To a large 12-inch skillet over medium heat, add olive oil. Once hot and shimmering, add the chicken in a single layer. (Depending on the size of the chicken breasts, you may need to work in batches.) Cook, uncovered, for 5 to 6 minutes, until golden brown. Flip and continue cooking for another 5 to 7 minutes, or until golden and the internal temperature reaches 165°F. Transfer the cooked chicken to a plate and loosely tent with aluminum foil.
Carefully discard all but 1 tablespoon of oil from the skillet and reduce heat to medium-low.
Add fresh thyme sprigs, diced shallot, and minced garlic. Cook for 1 minute, stirring often.
Add lemon zest, lemon juice, and chicken broth to the skillet. Use a wooden spoon to scrape up any browned bits from the bottom of the pan.
Let the mixture simmer for 2 to 3 minutes. Then, stir in the butter until melted and the sauce becomes glossy and slightly thickened.
Add the lemon slices to the skillet and let them warm through and slightly soften for 1–2 minutes.
Return the chicken to the pan, along with any juices. Spoon the sauce over the chicken and let it simmer for 1 more minute to reheat.
Serve the chicken over cooked white rice with sauce spooned on top.