Heat oven to 325ºF. Line a half-sheet pan with parchment paper and have a 10-inch loaf pan standing ready.
In the bowl of a food processor, combine the croutons, chili powder, thyme, black pepper, and cayenne pepper, if using. Pulse in short bursts until you achieve a coarse crumb, and then transfer mixture to a large mixing bowl. Add the onion, carrot, red pepper, and garlic to the now-empty food processor and pulse until mixture is finely chopped, but not pureed, scraping the bowl with a rubber spatula about halfway through the pulsing process. Transfer the vegetable mixture to the bowl with the breadcrumbs.
In small batches, add the meat to the food processor and pulse until it resembles a medium grind, 10 to 15 times.Add the meat to the mixing bowl with the breadcrumb-vegetable mixture. Add the salt and stir gently with your hands to combine. Add the egg and combine thoroughly, but avoid squeezing the meat.
Pack this mixture into the loaf pan to mold the shape of the meatloaf. Then, turn the meatloaf out of the loaf pan onto the prepared sheet pan. Insert a temperature probe at a 45-degree angle into the top of the meatloaf, avoiding touching the bottom of the tray with the probe. Set the probe alarm for 155°F and place the pan on the middle rack of the oven.
After 15 minutes, pull the meatloaf out of the oven and brush with the chipotle glaze. Return the meatloaf to the oven and cook until the probe alarm sounds at 155°F, about 1 hour and 15 minutes.
Rest the meatloaf for at least 20 minutes before slicing and serving.