Preheat oven to 350 degrees F. Prepare a baking dish with nonstick baking spray; set aside.
In a small skillet over medium heat, cook onions in oil until translucent, approximately 4-5 minutes.
Add rice, cheese, carrots, cashews, salsa, sea salt and pepper; cook for 3 minutes or until warm. Remove from heat.
Using a teaspoon, transfer mixture in each mushroom cap.
Place stuffed mushrooms in a single layer on the prepared baking dish. Bake for 10 minutes or until warm.
Remove from the oven; garnish with fresh chives & serve.