1. Preheat the oven to 350°F. Spray a 1-quart baking dish with nonstick spray.
2. Microwave the spinach according to package directions. Drain, let cool, then squeeze dry. Transfer the spinach to a large bowl.
3. Meanwhile, to make the topping, combine the Pepper Jack cheese and 2 tablespoons of the Parmesan cheese in a small bowl until blended.
4. Pulse the artichoke hearts in a food processor until smooth. Transfer the artichokes to the bowl with the spinach. Stir in the remaining Parmesan cheese, mayonnaise, ricotta, lemon juice, and ground red pepper until well mixed. Scrape into the prepared dish. Sprinkle evenly with the topping.
5. Bake, uncovered, until the filling is hot and the cheese is melted, about 30 minutes. Serve with the vegetable dippers.