Step 1

Cut all fish into ½" pieces. Add to medium bowl. Add juice of limes - fish should be completely covered by juice. Cover and refrigerate 3-4 hours.

Step 2

Remove fish from refrigerator. Fish should no longer be translucent and shrimp should be pink. Drain liquid from ceviche.

Step 3

Combine fish with mango, cilantro, onions, and tomatoes.

Step 4

Toast bread slices until golden brown. Divide avocado between toasts, mash with fork. Season with salt and pepper. Divide ceviche on toasts. Sprinkle with chili flakes if desired. Serve immediately.