Start the base: Set a large soup pot or Dutch oven over medium heat. Add the olive oil and let it heat until it looks loose and shiny, about 30 seconds.

Add the chopped onion to the pot. Cook, stirring often, until it softens and starts to turn lightly golden at the edges, 5 to 6 minutes.

Add the sliced garlic and smoked paprika to the pot. Stir for 30 seconds, just until the garlic smells fragrant.

Stir the tomato paste into the pot. Cook and stir for 1 minute, until the paste darkens a little and coats the onion.

Simmer the lentils: Add the potato pieces to the pot. Stir so the potatoes are coated in the tomato mixture.

Add the rinsed lentils to the pot. Stir once to mix them with the potatoes and onion.

Pour the broth into the pot. Raise the heat to high and bring the liquid to a boil.

When the stew reaches a full boil, lower the heat to medium-low so it bubbles gently. Cover the pot partway with a lid and cook for 18 minutes.

Check the lentils and potatoes. The lentils should be starting to soften, and the potatoes should be partly tender but not fully done yet.

Add the drained chickpeas to the pot. Keep the stew at a gentle simmer and cook for 7 to 10 minutes more, until the lentils and potatoes are fully tender.

Finish the stew: Use the back of a spoon to lightly crush a few potato pieces against the side of the pot. This thickens the broth slightly.

Add the tuna to the pot in large flakes. Stir very gently so the tuna warms through without breaking up too much, about 2 minutes.