Peel and grate carrots (on the large holes of a grater). Finely chop mushrooms and onion or pulse in a food processor.
In a large pan over medium-high heat, add olive oil. Once hot, add onion, garlic, mushrooms, and carrots. Sauté until veggies are tender and liquid has fully evaporated, about 5–7 minutes. Let cool 5–10 minutes in a large bowl.
Preheat oven to 375°F (190°C) and generously grease a regular-sized muffin tin with cooking spray.
To the cooled veggies, add all remaining meatloaf ingredients. Mix gently with hands. Avoid overmixing to avoid dense loaves.
Divide the mixture evenly into the prepared muffin tin. (You’ll use about a packed full 1/4 cup per cavity.) Bake for 15 minutes. Meanwhile, mix glaze ingredients with a pinch of salt and pepper. Glaze meatloaves evenly (use all the glaze) and return to oven for another 15 minutes.
Rest meatloaves for 5 minutes, then carefully lift out with a fork (use a knife to loosen edges if needed). Enjoy hot!
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Notes
Note 1: Panko is a type of Japanese breadcrumb known for its light, airy texture. Typically found next to breadcrumbs in the grocery store. You can swap regular dried breadcrumbs in this recipe, with a slight change in texture.Note 2: A good ketchup brand makes a world of difference; I love Heinz®!Storage: Cool and store in an airtight container in the fridge for up to 4 days. Freeze, individually wrapped, for up to 3 months.