Preheat oven to 400F. Brush or spray a large baking sheet with olive oil.

Prepare all the veggies: wash everything. Cube the sweet potatoes and carrots (make the carrots a bit smaller than the sweet potatoes, since they take longer to cook). Thinly slice the red onion. Separate the cauliflower into florets and cut into smaller pieces.

Place all the vegetables onto the roasting dish, spray with olive oil, season with salt and pepper. Roast at 400F for 15-20 minutes, or until desired done-ness. (Tip: I remove the red onion after 15 minutes, because it cooks the fastest, and then placed the rest of the veggies back into the oven.

While the vegetables are roasting, cook the buckwheat: Toast the uncooked buckwheat groats in a large dry pan for about 5 minutes over medium heat. This step is optional, but adds a nice nutty toasted flavor to the buckwheat.

Combine 3 cups of water and salt in a medium saucepan and bring to a boil. Add the 1.5 cups of buckwheat, stir, cover with a lid, lower the heat, and cook for about 10 minutes, or until the buckwheat is fully cooked (it should be a bit softer than cooked rice). If there is still water remaining when the buckwheat is done, strain it out in a colander.

While the buckwheat is cooking, prepare the tahini sauce: combine all the ingredients in a small bowl and stir gently until you get a smooth sauce. It might seem like the sauce is curdling, but keep stirring. Add a little extra water if it is too thick. Adjust to taste with more lemon juice or salt.

Toast the pepitas on a dry pan over medium heat for 2-3 minutes, or until they are toasted and fragrant. Remove from heat immediately so they don't burn.

Add 1 cup of cooked buckwheat to a bowl. Top with vegetables. Add some crumbled feta and chopped parsley. Drizzle with tahini sauce. Serve warm.