Thoroughly dry your chicken pieces and give them an even sprinkle of salt, pepper, and lemon zest.
Preheat oven to 425 degrees.
Chop the potatoes into roughly 1" cubes; the carrots into 2" pieces. Halve the onions and slice the halves into wide strips.
The garlic cloves get smashed and roughly chopped.
Slice the lemons into thick wheels and set the lemon slices aside until we have the veggies on the sheet pan.
In a very large bowl or container, mix the olive oil and seasonings with the veggies, adding the spinach at the end. Gently toss to coat the spinach and pour the veggie mix onto a sheet pan.
Top with lemon wheels, then top with chicken pieces. Sprinkle more lemon zest over top.
Bake for 30-35 minutes, check the temperature of the chicken; it's done when the thermometer reads 165. Let rest for 5-10 minutes.