Preheat your oven to 350°F (175°C) and lightly grease a loaf pan.
In a large bowl, mix together cooked lentils, breadcrumbs, onion, garlic, soy sauce, thyme, oregano, grated carrot, and chopped celery.
Transfer the mixture into the prepared loaf pan and press it down firmly to form a loaf shape.
Spread ketchup evenly over the top of the loaf.
Bake in the preheated oven for 1 hour, or until the top is golden and the loaf is heated through.
Let the vegan meatloaf cool for a few minutes before slicing and serving.