Prepare Parsley Arugula Pesto: Combine parsley, arugula, walnuts, Meyer lemon juice, olive oil, Dijon mustard, garlic, salt, and pepper in a food processor. Pulse until smooth, adding more lemon juice or olive oil for desired consistency. Taste and adjust seasoning.

Cook Buckwheat Soba Noodles: Bring water to a boil (without salt). Add soba noodles and cook for 5-6 minutes. Drain noodles and rinse under cold water. Set aside.

Cook Pancetta/Bacon (Optional): If using, cut pancetta or bacon into small pieces. Cook slowly until crispy. Drain on paper towels, discarding drippings.

Sauté Vegetables: Heat olive oil in a pan. Add chopped garlic, then onions, and cook until they begin to caramelize. Season with salt and pepper. Add red bell peppers and toss in the hot oil with the onions and garlic until slightly cooked. Turn off heat.

Combine and Serve: Toss together cooked noodles, sautéed garlic, onions, peppers, pancetta/bacon (if using), and 1-2 tablespoons of parsley arugula pesto. Taste and add more salt, pepper, or lemon juice if desired. Serve hot or cold.