Preheat the oven to 200°C (400°F).
Place the chicken thighs, baby potatoes, and onion slices in a baking dish. No need to peel the baby potatoes, but you can if you prefer. If some are quite large, cut them in half. Very small ones can be left whole. You can also use regular potatoes instead of baby potatoes. Just peel and quarter them. We enjoy it that way too!
Sprinkle the paprika, chili flakes, oregano, salt, and pepper over the ingredients. Drizzle with olive oil.
Use your hands to toss everything well, making sure all the pieces are evenly coated with the oil and spices. Arrange the chicken pieces skin side up and spaced apart so they’re not touching.
Cut a piece of baking paper to fit your baking dish. Crumple it into a ball, run it under water, then squeeze out the excess water. Use it to loosely cover the dish.
Bake for 45 minutes.
While it bakes, prepare the lemon garlic sauce: In a bowl, mix together the grated garlic, lemon juice, olive oil, and water.
After 45 minutes, remove the dish from the oven and discard the baking paper. Pour the sauce evenly over the chicken and potatoes. Try to avoid leaving garlic pieces on top of the chicken or potatoes, as they can burn easily. Use a spoon to gently push any exposed garlic into the sauce in the bottom of the pan.
Return to the oven and bake uncovered for another 25 minutes, or until the chicken is golden and cooked through.
Garnish with chopped parsley and fresh lemon slices before serving, if desired.