Preheat the oven to 425°F (220°C) and line a large rimmed baking sheet with aluminum foil.
In a large resealable bag or bowl, combine 2 tablespoons olive oil, soy sauce, lemon juice, lemon zest, 3 minced garlic cloves, and 2 teaspoons chopped thyme.
Add the 4 boneless skinless chicken breasts to the marinade, seal, and refrigerate for 20–30 minutes.
Meanwhile, in a large bowl mix 2 tablespoons olive oil, 3 minced garlic cloves, 1 1/2 teaspoons smoked paprika, 1 teaspoon salt, and 1/4 teaspoon pepper.
Toss 1.5 pounds halved baby potatoes in the spiced oil until evenly coated, then spread the potatoes in a single layer on one side of the prepared sheet pan.
Remove the chicken from the marinade (discard the marinade), place the breasts on the empty side of the sheet pan, season both sides with salt and pepper, and top each breast with a lemon round.
Bake for 15 minutes, then remove the pan and toss the potatoes to promote even browning.
Return the pan to the oven and bake an additional 15–20 minutes, or until the chicken is cooked through and the potatoes are tender when pierced with a fork.
Remove from the oven and serve the chicken and potatoes warm.