Wash and dry produce. Halve, peel, and dice onion into roughly 1/2-inch pieces. Trim, peel, and halve carrots lengthwise; slice crosswise into 1/4-inch half-moons. Halve celery lengthwise; thinly slice crosswise. Drain and rinse lentils.

In a medium pot (use a large pot for 4 servings), heat a large drizzle of oil over medium-high heat. Add onion, carrot, celery, salt, and pepper; cook, stirring occasionally, until veggies are slightly softened, 2-3 minutes. Add garlic powder, chili powder, cumin, and tomato paste; cook, stirring, until fragrant, 30-60 seconds.

Stir in 21/2 cups of water (5 cups for 4 servings), lentils, and stock concentrates, scraping any browned bits from bottom of pot. Bring to a simmer; cook, uncovered, until flavors meld, 5-7 minutes.

Meanwhile, empty kidney beans (and their liquid) into a medium bowl. Mash using a potato masher until beans are a smooth as possible (this will help to thicken the soup). Stir beans into soup; return to a boil and reduce heat to a simmer. Continue to cook, stirring occasionally, until soup thickens, 3-5 minutes.

While soup is simmering, thinly slice chives.

When soup is done, taste and season with salt and pepper, if needed. Divide soup between bowls; garnish with a dollop of sour cream and sprinkle chives over top. Serve.