Wash the mixed greens thoroughly and pat them dry.
Peel the ripe mangoes and slice them into thin wedges.
In a large bowl, combine the mixed greens, mango slices, and diced red bell pepper.
Thinly slice the red onion and add it to the bowl.
Chop the fresh cilantro and sprinkle it over the salad.
In a small bowl, whisk together the lime juice and olive oil.
Pour the dressing over the salad and toss gently to combine.
Season with salt and pepper to taste.
If using, slice the avocado and arrange it on top for garnish.
Serve immediately or chill in the fridge for 10 minutes before serving.