Marinate the sliced red onion in the lime juice and lime zest for 30 minutes in a small bowl.
Meanwhile, caramelize the corn by heating a sauté pan over medium-high heat with 1 tablespoon olive or canola oil. Add the corn and the sugar and sauté until the corn is golden brown. Remove from heat and let cool.
Combine the canned beans, mango, red bell pepper, jalapeno, cilantro, avocado and garlic with the marinated onions and cooled corn. Toss gently and add salt to taste.