Heat olive oil in a large skillet over medium-high heat.
Season chicken with salt and pepper, then sear in the skillet until browned, approximately 5 minutes. Remove chicken and set aside.
In the same skillet, add onion and bell pepper; sauté for 4 minutes until softened.
Add garlic, cumin, and paprika; cook for 1 minute until fragrant.
Stir in rinsed quinoa and chicken broth, scraping the bottom of the pan to deglaze.
Return chicken to the skillet, bring to a boil, then reduce heat to low and cover.
Simmer for 15 minutes or until quinoa is tender and liquid is absorbed.
Fold in baby spinach and lemon juice until spinach is wilted. Serve immediately.