Preheat the oven to 350F. Lightly butter/grease a standard loaf pan (line with parchment if you want to ensure it comes out easily).
In a high-speed blender, add 1 cup of seeds, buckwheat flour, oats, baking soda, and salt. Blend on high until a fine flour forms. Scrape under the blade, if needed. It’s okay if there are some bigger chunks of seeds.
In a large bowl, add the olive oil, vinegar, and eggs and whisk until smooth. Stir in the veggies, and 1 cup cheddar cheese. Add the dry ingredients to the bowl and use a rubber spatula to combine until no flour remains (use some muscle, the mixture will be dry/thick).
Transfer to the loaf pan and spread out into an even layer. Top with remaining ½ cup cheese, then sprinkle on remaining ¼ cup seeds .
Bake for about 50-60 minutes, or until a toothpick, cake tester, or knife comes out clean.
Carefully remove from pan and transfer to a cooling rack. Let cool for at least 10 minutes, then slice and serve warm topped with butter, if desired. Use the toaster to warm up leftovers.