Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Add diced onion and sauté for 3-4 minutes until softened and fragrant, stirring occasionally to prevent burning.

Stir in minced garlic and sliced mushrooms, cooking for 2-3 minutes until mushrooms release their moisture and begin to brown. The mushrooms add incredible depth that becomes the backbone of this warm dinner.

Add diced bell peppers and zucchini to the pot, stirring well to combine all the cozy meatless weeknight dinner recipe components. Cook for another 2 minutes while the vegetables warm through and begin releasing their natural juices.

Pour in the can of diced tomatoes with their juice, vegetable broth, and dried lentils. Add oregano, basil, salt, and pepper, stirring everything together thoroughly. Bring to a boil, then immediately reduce heat to medium-low.

Simmer for 25-28 minutes uncovered, stirring occasionally, until lentils are tender but not mushy. The broth should reduce slightly while the lentils absorb all those rich flavors.

Stir in the fresh spinach during the final minute of cooking, allowing it to wilt completely into the warm mixture. The spinach adds brightness and final nutrition to the dish.

Taste and adjust seasonings as needed—add more salt, pepper, or herbs based on your preference. Divide into bowls and top each serving with grated parmesan cheese for richness.