Bring a medium sauce pot of generously salted water to a boil. Add the rigatoni and cook until just tender, 11 to 13 minutes. Drain, reserving ½ cup [1 cup] pasta cooking water. While the water heats and the rigatoni cooks, start preparing the stroganoff.

• Peel and coarsely chop enough onion to measure ¼ cup [½ cup].
• Thinly slice the mushrooms.

In a small bowl, stir or whisk together the almond milk and mushroom stroganoff blend.

In a large frying pan over medium-high heat, warm 2 to 3 teaspoons oil until hot but not smoking. Stir in the onion, season with salt and pepper, and cook until starting to soften, 1 to 2 minutes. Add the mushrooms, season with salt and pepper, and cook, stirring occasionally, until the mushrooms are browned and tender, 3 to 4 minutes.
Add the almond milk mixture and reserved pasta cooking water and bring to a boil, then reduce to a simmer. Cook, stirring constantly, until the sauce thickens, 1 to 2 minutes.

• Strip the parsley leaves from the stems; coarsely chop the leaves for garnish.

To the pan with the sauce, stir in the rigatoni and cook until heated through, 1 to 2 minutes. Working in batches if needed, stir in the spinach and cook until just wilted, about 1 minute. Remove from the heat and stir in the peas; season to taste with salt and pepper.

Transfer the stroganoff to individual bowls. Drizzle each with 1 to 2 teaspoons oil, garnish with the parsley, and serve.