In a blender, purée all the ingredients. Pour the marinade into a bowl. Add the meat and toss to coat. Cover and let marinate in the refrigerator for 3 to 6 hours.
In a bowl, combine all the ingredients. Season with salt and pepper. Cover and refrigerate for 1 hour.
Preheat the grill, setting the burners to high.
Meanwhile, in a bowl, combine the sugar and salt. Add the onions and toss to coat. Place the onions in the centre of a sheet of lightly oiled aluminum foil. Close the foil, sealing well. Bake for about 35 minutes or until the onions are tender and lightly browned. Set aside.
In a bowl, mash the avocado flesh with a fork. Add the remaining ingredients and stir to blend. Season with salt and pepper.
Drain the meat. Thread 4 cubes of meat on each skewer, alternating with 3 pieces of bell pepper. Season with salt and pepper.
Cook the beef skewers for about 1 minute on all four sides, for medium-rare or cook the chicken skewers for 2 to 3 minutes on all four sides.
Warm the tortillas on the grill.
Place the skewers on hot tortillas and remove the sticks.
Place the toppings in the centre of the table and let your guests garnish their fajitas to their taste. Serve rolled.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.