Prepare mise en place: dice carrots, celery and onion; mince garlic; measure spices and have cooked lentils and rice ready. Good mise en place speeds the cook and ensures ingredients hit the pan at the right time.

Heat a heavy 4–5 quart Dutch oven or large saucepan over medium heat and add 2 tablespoons olive oil. When the oil shimmers (but before it smokes), add the diced carrots and celery. Sauté 4–5 minutes until they begin to soften and develop slight color — this gentle browning builds sweet, savory depth in the finished stew.

Add the diced onion and a pinch of salt to the pan and continue to cook for 3–4 minutes until the onion is translucent. The salt helps draw moisture from the onion and vegetables so they cook evenly and brown more reliably.

Push the vegetables to one side of the pan, add the remaining 2 tablespoons olive oil to the cleared space, then add the minced garlic, ground cumin and smoked paprika. Toast the spices and garlic briefly — 30–45 seconds — stirring constantly. Toasting spices in oil 'blooms' their essential oils, intensifying aroma and flavor; avoid burning the garlic (it will turn bitter) by stirring and removing from direct heat briefly if it darkens.

Stir the spices into the vegetables so the orange-red paprika and cumin coat the carrots and celery. Add the canned diced tomatoes with their juices and scrape up any browned bits from the bottom of the pot (those fond bits hold a lot of flavor). The tomatoes add acidity and body; deglazing integrates those caramelized flavors.

Pour in 3 cups of vegetable or chicken broth and bring to a gentle simmer. Add the cooked lentils. If you prefer a looser stew, add up to 1 additional cup of broth. Simmer uncovered for 8–10 minutes so the flavors meld and liquids reduce slightly. Simmering (rather than boiling) concentrates flavor and prevents the lentils from breaking down too much.

Taste and season with kosher salt (start with the recipe's 1 1/2 teaspoons total) and freshly ground black pepper. Adjust seasoning as needed — remember that the rice will be neutral so the stew should be slightly more seasoned than you think when tasted alone.

Stir in the cooked brown rice and baby spinach. The rice will absorb some liquid and knit with the lentils; the spinach wilts quickly. Cook just 2–3 minutes more until rice is heated through and greens are fully wilted. If using kale, simmer 4–6 minutes to soften it. Adding rice at the end preserves its texture and prevents it from becoming gummy.

Finish off heat with 1 tablespoon butter or a drizzle more olive oil and 1 tablespoon fresh lemon juice to brighten the stew. The fat enriches mouthfeel while the acid lifts and balances flavors. Give a final taste and correct salt and pepper.

Serve the stew in warmed bowls, spooning the lentil-vegetable ragout over the rice (or mix together). Garnish with an extra drizzle of olive oil and, if you have it, chopped parsley or a dollop of yogurt. The stew keeps 3–4 days in the fridge and freezes well.