Step 1

Toss shallot, garlic, chile, lime juice, and salt in a medium bowl. Add mangoes and cucumber and toss again. Cover; let sit at room temperature until shallot and cucumber are softened and juicy and flavors come together, 45–60 minutes.

Step 2

To serve, add cilantro to chow and toss well; season generously with pepper.

Step 3

Chow (without cilantro) can be made 3 hours ahead. Cover and chill.