Add all of the ingredients to a blender or blending container (if using an immersion blender) and mix on high speed until very smooth. Taste and add maple syrup or honey if needed. Serve immediately.
Red lentils usually take about 15 minutes to cook. Make sure to cook them in unsalted water and drain well before adding to the smoothie. Rinse with cold water if using immediately.Omit the lentils: if you want a plain strawberry mango smoothie, leave the lentils out. You could sub hemp hearts if you don't have cooked lentils on hand.