Prepare lentils: Rinse the lentils, remove odd pieces. In large pot add 2 1/2 cups water/broth with lentils. Bring to a boil, reduce heat, cover and simmer for about 35 – 40 minutes, stirring occasionally. It’s ok if they get mushy, we are going to roughly puree 3/4 of the mixture when cooled. Once done, remove lid and set aside to cool (there should only be a little bit of water so do not drain), lentils will thicken a bit upon standing, about 15 minutes is good.
Preheat oven to 350 degrees.
Make flax egg: In small bowl combine flaxseed meal and 1/3 cup water, set aside for at least 10 minutes, preferably in the refrigerator. This will act as a binder and will thicken nicely upon sitting.
Saute vegetables & spices: In saute pan heat oil or water over medium heat. Saute garlic, onion, bell pepper, carrots and celery for about 5 minutes. Add spices mixing well to incorporate. Set aside to cool.
Mash the lentils: Using an immersion blender, food processor, back of a fork or potato masher, blend 3/4 of the lentil mixture. For me this was an important part, I tried it other ways and this worked to help as a binder. If using an immersion blender, tilt the pot slightly to the side for easier blending.
Assemble lentil loaf: Combine sauteed vegetables with the lentils, oats, oat flour and flax-egg, mix well. Taste, adding salt and pepper as needed, or any other herb or spice you might like. Place mixture into a 9×5 loaf pan lined with parchment paper, leaving it overlapping for easy removal later. Press down firmly filling in along the edges too.
Glaze: Prepare your glaze by combining all ingredients in a small bowl, mix until incorporated. I recommend making each tablespoon heaping so you have plenty of this great sauce on top (if using tomato paste and mixture is too thick, add a teaspoon of water, or a little extra vinegar & syrup). Spread evenly over top the loaf.
Bake: Place in center of the oven, and bake in oven for about 45 – 50 minutes. Let cool a bit before slicing.