Sauté the base vegetables. Place a large pot over medium heat and add the olive oil. Once warm, stir in the diced onion, carrots, and celery. Season lightly with salt and pepper, and cook for about 8 minutes, stirring occasionally, until the vegetables begin to soften.

Build the flavor. Add the mushrooms, sliced garlic, thyme, oregano, and sage to the pot. Cook for another 3–4 minutes, stirring frequently, until the mushrooms release moisture and the mixture becomes fragrant.

Add the thickener. Sprinkle the flour over the vegetables and stir well to coat everything evenly. Cook for about 1 minute to remove the raw flour taste and help thicken the stew later.

Deglaze the pot. Pour in the balsamic vinegar and soy sauce. Stir well, scraping the bottom of the pot to lift any flavorful browned bits. This step adds depth and richness to the stew.

Add remaining ingredients. Stir in: potatoes, lentils, tomato sauce, vegetable broth, bay leaves. Season again with a pinch of salt and pepper.

Simmer gently. Bring the mixture to a gentle simmer over medium-high heat, stirring occasionally to prevent the lentils from sticking. Reduce the heat to low and let the stew cook uncovered for 10–15 minutes, or until: the potatoes are tender, the lentils are soft.

Taste and finish. Remove the bay leaves. Taste the stew and adjust seasoning with additional salt and pepper if needed. Ladle into bowls and garnish with fresh parsley if desired.