Begin by prepping the ingredients. Dice mangos and tomatoes into 1/4-1/2" chunks. Seed the tomatoes before dicing. Remove the veins and seeds from the jalapeno and mince. Chop the red onion and green onions to 1/4" chunks or smaller. Chop the cilantro. Mix all in a large bowl.
In a small bowl, combine the citrus juice, salt, and oil. Mix until the salt dissolves. Pour over the mango mixture and stir well. Let sit, covered, at room temperature for about 30 minute to 1 hour for flavors to develop. Salsa is best within 8 hours of making. If desired, store tightly covered in the refrigerator for up to 1 day.