Cut the mango flesh away from the pit, score it in a crosshatch pattern, and scoop out 1/4-inch dice. Halve and pit the avocados, then cut into similar-sized dice. The pieces should be small enough to scoop but large enough to hold their shape.

Mince the jalapeño fine, removing seeds and white pith if you prefer less heat. Finely dice the red onion - you want about 2 tablespoons after dicing. Chop the cilantro, including tender stems.

In a medium bowl, gently fold together mango, avocado, jalapeño, red onion, and cilantro. Drizzle with lime juice and sprinkle with salt and cumin. Fold carefully to avoid mashing the avocado. Taste and adjust salt or lime - the salsa should taste bright and slightly salty since it will be eaten with chips.

Let sit at room temperature for 10 minutes if possible - this allows the flavors to meld. Serve immediately, or press plastic wrap directly onto the surface and refrigerate up to 2 hours.