Heat oil in a large skillet over medium high heat. Add onion and cook, stirring occasionally until transparent, 8 to 10 minutes. Add mushrooms and cook until softened, 4 to 5 minutes more. Add carrots and chopped peppers, cook until just softened, then add parsley and spinach (in batches, if needed). Let spinach wilt then stir in cinnamon, cumin and cooked quinoa and toss gently to combine. Add salt, pepper and cashews and cook 1 to 2 minutes more. Set aside to let filling cool until just warm.

Meanwhile, preheat oven to 350?F. Grease a 9- x 13-inch baking pan with oil then set aside.

Divide quinoa mixture evenly among remaining 6 bell peppers, gently packing it down and making sure to fully fill each pepper. Top each pepper with its reserved top then arrange them upright in prepared pan. Cover snugly with foil and bake, checking halfway through, until peppers are tender and juicy and filling is hot throughout, about 1 hour. Transfer to plates and serve