In a small bowl or measuring cup, whisk together the coconut aminos, 2 Tbsp avocado oil, sesame oil, minced garlic, fish sauce, and sriracha (if using) to make the marinade.
Place the chicken thighs in a large zip-top bag or shallow dish and pour in the marinade. Seal or cover and turn to coat. Marinate at least 20 minutes or up to 24 hours in the refrigerator.
Preheat the oven to 425°F (220°C).
Prepare the vegetables: spread the red bell pepper matchsticks, sliced red onion, chopped yellow squash, chopped broccoli, and chopped carrots in a single layer on a large rimmed baking sheet.
Drizzle the vegetables with 2 Tbsp avocado oil for the vegetables, sprinkle with garlic powder and sea salt, and toss with your hands or tongs until evenly coated.
Arrange the marinated chicken thighs on top of the vegetables or nestle them into openings on the sheet. Discard any remaining marinade.
Bake on the upper-middle oven rack for 25 to 30 minutes, stirring the vegetables once halfway through, until the vegetables are tender and the chicken reaches an internal temperature of 185–205°F in the thickest part.
Remove from the oven and let rest briefly, then serve the chicken with the roasted vegetables.