Preheat oven to 400 F. Line rimmed baking sheet with parchment paper and set aside.

In food processor, pulse almonds until very finely chopped. Add pumpkin seeds and sunflower seeds; pulse until coarsely chopped. Transfer mixture to large bowl. Place carrots in food processor; process until very finely chopped. Add carrots, garlic, thyme, cumin, black pepper, salt, eggs, and egg whites to bowl and mix well.

Press carrot mixture onto prepared baking sheet in 1/2 inch thick rectangle layer. Bake for 25 minutes, or until flatbread is firm and darkened around edges. Cool in pan for at least 5 minutes before slicing into 8 to 10 pieces.

Reduce oven temperature to 325 F. Line baking sheet with clean parchment paper. Place salmon on sheet, skin side down, and season with salt and pepper; bake until barely cooked through in middle, about 15 minutes. Let rest for 5 minutes before breaking flesh into large chunks.

Spread mustard on carrot bread slices. Top with arugula, salmon, and roasted red pepper. Squeeze lemon juice over top.