Bring a medium sauce pot of generously salted water to a boil for the penne. Separate the penne so the noodles don’t clump together during cooking.

• Let the creamy feta sauce base come to room temperature.
• Cut the cauliflower into 1-inch florets, discarding any leaves or thick stalks.
• Peel and finely chop the shallots.
• Cut the tomatoes in half.
• Strip the parsley leaves from the stems; coarsely chop the leaves.

To the pot of boiling water, stir in the penne and cook, stirring occasionally, until just tender, 3 to 5 minutes. Drain the penne, reserving ¼ cup [½ cup] pasta cooking water. Return the penne to the pot; drizzle with about 1 tablespoon oil and toss to keep the noodles from sticking.
While the penne cooks, start the sauce.

In a large frying pan over medium-high heat, warm 1 to 2 tablespoons oil until hot but not smoking. Stir in the shallots and cook until fragrant, about 1 minute. Add the cauliflower, season with salt and pepper, and cook, stirring occasionally, until the cauliflower starts to soften, 2 to 3 minutes [3 to 4 min]. 
Add the tomatoes, parsley, and peas and cook, stirring occasionally, until the tomatoes start to soften, 2 to 3 minutes. Stir in the penne, reserved pasta cooking water, creamy feta sauce base, and spinach (the spinach in batches if needed) and cook until the spinach is just wilted, about 1 minute. Remove from the heat and season to taste with salt and pepper.