Prepare the Oranges: Peel the oranges and remove the white pith. Carefully separate the orange sections from their membranes and cut them into small pieces. Measure 3 cups and place them in a large mixing bowl.
Chop the Red Onion: Peel and finely dice the red onion into small, even pieces. Measure ¼ cup and add it to the prepared oranges.
Dice the Avocado: Cut the avocado in half and remove the pit. Scoop out the flesh and dice it into small cubes. Measure ½ cup and add it to the mixing bowl.
Prepare the Serrano Chile: Finely chop the serrano chile into small pieces. Add the chopped chile to the orange, onion, and avocado mixture.
Add the Lemon Zest: Using a citrus zester or fine grater, grate only the yellow outer peel of a fresh lemon, avoiding the bitter white pith. Measure 1 teaspoon and add it to the bowl.
Add the Lime Zest: Grate the green outer peel of a fresh lime, avoiding the white pith. Measure 1 teaspoon and sprinkle it over the salsa ingredients.
Season with Salt: Add ¾ teaspoon salt evenly over the mixture.
Gently Mix the Salsa: Using a spoon, gently fold all the ingredients together until the oranges, avocado, onion, serrano chile, and citrus zest are evenly combined. Avoid stirring too vigorously to keep the fruit pieces intact.
Serve the Salsa: Transfer the citrus avocado salsa to a serving bowl and serve immediately while the ingredients are fresh and juicy.