Bring a large pot of heavily salted water to a boil. Add a splash of oil to the water then cook the spaghetti according to the pasta directions. Drain.
Heat olive oil in a large skillet over medium-high heat. Add onion and saute until fragrant, about 2 minutes. Add garlic and saute for another minute.
Add chicken and 1 tablespoon lemon juice to pan. Cook, stirring occasionally about 5 to 6 minutes until chicken is no longer pink in the center and the juices run clear.
Reduce heat to medium-low; add artichoke hearts, roasted red peppers, tomato, feta cheese, parsley, remaining lemon juice, oregano, and cooked elbow pasta. Stir until heated, about 2 to 3 minutes. Season with salt and pepper.