Sauté Aromatics: Warm the oil in a large heavy bottomed pot over medium heat. Add the onion and sauté for 7 to 10 minutes, until the onion is translucent and golden. Add the garlic and ginger and sauté for 1 minute, until fragrant. Add the curry powder and tomato paste and sauté for an additional 1 to 2 minutes, until fragrant and beginning to stick to the bottom of the pan.
Lentils: Add a splash of the vegetable broth and scrape any browned bits off the bottom of the pan. Add the bell pepper, lentils, and pumpkin and the remaining broth and mix well.
Simmer: Bring to a simmer over high heat. Reduce the heat to medium (or medium low if it starts to splatter) and simmer for 25 to 30 minutes, stirring occasionally, until the lentils are cooked. If the curry gets too thick for your liking you can thin it out with warm water in 1/2 cup increments.
Tahini “Cream”: In the meantime, add the tahini and lemon juice to a small bowl. Mix together – the tahini will thicken. Slowly pour 1/4 cup of water into the mixture while you mix; the tahini sauce should lighten and loosen into the consistency of a thick pancake batter. If your tahini is on the thicker side, you may need to add more water. Set aside.
Final Touches: Turn the heat off once the lentil curry has cooked to your liking, then add the tahini cream and mix well, until combined.
Serve & Store: Serve warm, topped with cilantro, over cooked rice and with naan, or as desired. Store any leftovers in the refrigerator in an airtight container for up to 5 days, or you can freeze leftovers for up to 2 months.