Heat 1/4 cup (60 mL) butter in a large skillet over medium-high heat. Stir in onions and cook for about 5 minutes, until they are translucent. Stir in garlic, ginger, brown sugar, chili powder, curry powder, salt, and pepper. Cook for another 1-2 minutes until mixture is fragrant and garlic is golden. Remove from heat.

In a 4 or 5-quart slow cooker, add onion mixture, diced tomatoes, chicken stock, and peanut butter. Stir together, cover and cook 5-8 hours on low.

With an immersion blender, puree sauce until smooth.

In a large skillet, heat remaining butter over medium heat. Add half the chicken, season with salt and pepper and cook until each side is golden brown, about 3-4 minutes per side. Repeat with remaining chicken. When chicken is browned, add it to the slow cooker, along with the lentils.

Cover, and cook for another 30 minutes on high, until chicken is fully cooked and no longer pink inside.

Stir in whipping cream, cilantro, and adjust seasonings with more salt and pepper, if needed.

Serve over steamed rice, with naan bread on the side.