Karashi Mentaiko (Spicy Cod Roe) and Spinach Spaghetti

Ingredients (10)

• 1 teaspoon olive oil
• 1 1/2 teaspoons unsalted butter
• 1/4 cup chopped yellow onion
• 1/2 cup baby spinach
• 1 to 2 cups cooked spaghetti, regular or or whole wheat
• 1 ounce cod roe (karashi mentaiko, mentaiko, or tarako)
• 1 dash white pepper
• 1 sheet kizami nori
• Dried seaweed, sliced, for garnish, optional
• Shiso, cut into a chiffonade, for garnish, optional