In a large skillet or pot over medium-high heat, add the ground turkey and chopped yellow onion, cooking until the turkey is fully browned and the onion is soft.
Stir in the minced garlic and ground cumin, sautéing for about 60 seconds until the mixture becomes fragrant.
Add the dry green lentils, dry brown rice, and vegetable broth to the pot, then bring the liquid to a gentle boil.
Lower the heat to a simmer, cover with a tight-fitting lid, and cook for 35 to 40 minutes until the lentils and rice have absorbed the broth and are tender.
Remove from heat, then fold in the baby spinach, sea salt, and black pepper, allowing the residual heat to wilt the greens.
Stir in the fresh lemon juice to provide a bright finish and serve immediately in a warm bowl.