Firmness is the key to this salad — you want the mangoes and avocado to have character. The mangoes shouldn't be fibrous and the avocados should be uniformly green and not mushy at all. You should have to bite into both.
Two alternate versions of this salad work well too. Thinly-sliced Fresno peppers are a nice touch of color, and if you can find them, Champagne mangoes take the salad to the next level — they're a little more tart than sweet. You're going to get some sweetness from these shrimp anyway.
Also consider grilling the fruit. A little char on the mango, avocado, and tomato will bring another whole dimension to the salad.
Heat up your grill or grill pan. Place the mango and avocado in a bowl and squeeze the lemon juice over them. Toss gently. Add tomato, julienned jicama, and thinly-sliced jalapeño. Lightly drizzle olive oil. Season with salt and pepper. Set aside.
Toss Mayan shrimp with olive oil, salt, pepper, and red pepper flakes. When your grill is super hot place them on. Turn in a minute to a minute and a half (don't overcook!). Plate shrimp on top of salad and dig in.