Preheat oven to 425°. On a large baking sheet, toss potatoes and onion with 1 tablespoon olive oil; season with salt and pepper. Bake until tender, 20 to 25 minutes.
Meanwhile, in a large skillet over medium-high heat, heat 1 tablespoon olive oil. Season chicken with garlic powder, ginger, salt, and pepper. Cook chicken, turning occasionally, until golden and no longer pink, about 8 minutes per side. Transfer to a cutting board and let rest 10 minutes, then thinly slice.
In a small bowl, whisk garlic, lime juice, peanut butter, honey, and soy sauce until combined. Whisk in sesame oil and remaining 1 tablespoon olive oil until smooth.
Divide rice among bowls. Top with potato mixture, chicken, avocado, and spinach. Sprinkle with cilantro and sesame seeds. Drizzle with dressing.
