Step 1: Preheat oven to 375°F (190°C). Unroll crescent dough onto a large baking sheet and press seams together firmly to form a solid rectangular crust. Bake for 10-12 minutes, or until golden brown. Let cool completely on the baking sheet.
Step 2: In a medium bowl, beat softened cream cheese until smooth. Add mayonnaise and ranch dressing mix, mixing until well combined and creamy.
Step 3: Spread the cream cheese mixture evenly over the cooled crescent roll crust, going all the way to the edges.
Step 4: In another bowl, combine the finely chopped broccoli, carrots, red bell pepper, green onions, and cucumber. If using, mix in shredded cheddar cheese.
Step 5: Evenly sprinkle the chopped vegetable mixture over the cream cheese layer. Gently press down so the vegetables adhere to the spread.
Step 6: Cover loosely with plastic wrap and chill for at least 30 minutes before serving. Cut into squares or rectangles and serve cold.