Cook the lentils. Cook the lentils in lightly-salted water according to package directions until tender. Pour into a fine-mesh strainer and rinse with cold water until chilled, then drain off any extra water.
Toss. Combine the lentils, avocado, mango, red onion, baby spinach, mint, almonds and feta in a large mixing bowl and drizzle evenly with the dressing. Toss gently until combined. Taste and season with salt and pepper as needed.