Preheat your oven to 425°F (220°C). Spread the cubed sweet potatoes on a baking sheet. Drizzle with 1 tablespoon of olive oil, and season with salt and pepper. Toss to coat evenly.

Roast the sweet potatoes in the preheated oven for 25-30 minutes, or until they are soft and slightly caramelized, stirring halfway through.

While the sweet potatoes are roasting, rinse the quinoa under cold water. Add the quinoa to a medium saucepan with 2 cups of water and a pinch of salt. Bring to a boil over high heat, then reduce to a simmer, cover, and cook for about 15 minutes, or until the quinoa is fluffy and all the water is absorbed. Remove from heat and let it sit, covered, for 5 minutes, then fluff with a fork.

In a small bowl, combine the remaining 1 tablespoon of olive oil, lemon juice, tahini, minced garlic, and a pinch of salt and pepper. Whisk until smooth to make the tahini-lemon dressing. Adjust seasoning to taste.

Heat a grill pan over medium-high heat. Season the chicken breasts with salt and pepper. Grill the chicken for about 5-7 minutes on each side or until the internal temperature reaches 165°F (75°C). Remove from the grill and let rest for a few minutes before slicing.

In a large bowl, combine the baby spinach, cooked quinoa, and roasted sweet potatoes. Drizzle with half of the tahini-lemon dressing and toss gently to combine.

Divide the mixture into serving bowls. Top each bowl with sliced grilled chicken, diced avocado, and a sprinkle of crumbled feta. Drizzle with the remaining tahini-lemon dressing before serving.