Cook the sliced garlic in the oil until it is brown, then set aside to cool.
Preheat a grill.
In a mixing bowl, combine onions, tomatoes, jalapeno, zucchini, and leeks, and pour half of the remaining garlic oil on top. Season, to taste, with salt and pepper.
Grill the garlic-oil vegetables over high heat until soft, and then cool.
Season the tenderloin and rub with some of the oil mixture.
Grill the meat for 4 to 5 minutes per side, and set aside to rest.
Cut all the grilled vegetables and the red pepper into large pieces. Toss with the remaining garlic oil, basil, and season, to taste, with salt and pepper.
Plate the meat with the vegetables.