Combine lentils and 5 cups of water into large pot, bring to a boil. Reduce to simmer and cook until 10-15 minutes, or until tender. Drain.

Meanwhile, heat oil in large skillet over medium-high heat. Add mushrooms, onion, and peppers and cook stirring occasionally 4-5 minutes or until softened. Add garlic, chilli powder, mustard, Worcestershire, ketchup, pumpkin, salt, pepper and lentils. Cook for 3 minutes, stirring occasionally.

Microwave pitas on HIGH for 20 seconds. Place filling on one half of each pita and fold in half.