Grilled Ratatouille

4 garlic cloves, crushed and peeled 

1/2 cup extra-virgin olive oil  

1 1/8 tsp. plus 1/2 tsp. salt 

1 large globe eggplant, about 1 1/2 lb., cut into slices 1/2 inch thick 

Canola oil for brushing 

1 large yellow onion, cut crosswise into rounds 1/4 to 1/2 inch thick 

1/8 tsp. freshly ground black pepper 

2 large red bell peppers  

2 zucchini, about 1 lb. total, halved lengthwise  

3 large tomatoes, about 1 lb. total, halved crosswise 

1/2 cup fresh basil leaves  

1/4 tsp. red pepper flakes