In a medium bowl, whisk together garlic, red wine vinegar, thyme, agave nectar, Worcestershire sauce, salt and pepper. While whisking, slowly pour in the olive oil.
Place the tri-tip steak in a large resealable plastic bag. Add the marinade, seal the bag and massage the meat to coat it with the marinade.
Refrigerate for at least 6 hours and up to 12 hours.
Remove the steak from the refrigerator 30 minutes prior to grilling to allow the meat to come to room temperature.
Preheat the grill to medium-high heat and lightly oil the grill.
Place the steaks on the grill and cook until desired degree of doneness is reached, about 5 minutes per side, depending on the thickness of the steak. Remove steak from the grill and let rest for 10 minutes before slicing.
The Pesto:
Place roasted red bell peppers in the bowl of a food processor. Add slivered almonds, garlic, cilantro, Parmesan cheese, and lime juice. Pulse until combined.
While the food processor is running, slowly pour in olive oil. Season with salt and pepper. Set the pesto aside.