Preheat the oven to 180 degrees Celsius (356 F). Line a large sheet pan with parchment paper.
If making homemade pesto, add all of the pesto ingredients to a food processor and blend on high until smooth. Remove 1/2 cup of pesto for this recipe.
Add half of the pesto to a large mixing bowl along with half of the olive oil. Stir to combine.
Add the chopped vegetables to the bowl and toss to coat evenly in pesto. Tip vegetables out onto sheet pan and spread out in a single layer.
Add the remaining pesto to the bowl along with the remaining olive oil. Stir to combine. Add the chicken thigh fillets to the large bowl and toss to marinate the chicken thigh evenly. Place the chicken thighs between the vegetables on the tray so that the vegetables and chicken are still in a single layer. Season liberally with salt and pepper.
Place the tray into the oven on the middle shelf to bake for 45 minutes.
Once baked, remove from the oven. Immediately add the baby spinach leaves to the pan and stir through until the baby spinach is wilted. Serve warm.
Notes
Storage
Store leftovers in an airtight container in the fridge for up to 3 days. Reheat before eating. This recipe is made using my cilantro walnut pesto, however you can use a basil pesto or store bought pesto.