Coat a large nonstick skillet with cooking spray; place over medium-high heat until hot. Add bell pepper and onion; sauté 4 minutes or until tender. Combine bell pepper mixture, tomato paste, 1/8 teaspoon salt, and black pepper in food processor, and process until smooth. Return mixture to skillet, and cook over medium-high heat 3 minutes or until thickened. Spoon mixture into a bowl, and let cool; cover and chill.
Place cucumber on several layers of paper towels; cover with additional paper towels, pressing until barely moist. Combine the cream cheese, blue cheese,1/8 teaspoon salt, and ground red pepper in a small bowl, stirring until smooth. Stir in cucumber; cover and chill.
Spread 2 tablespoons bell pepper mixture over each of 8 slices of white bread; top each with a slice of wheat bread. Spread 2 tablespoons cucumber mixture over each slice of wheat bread; top with remaining white bread.
Trim crusts from sandwiches. Cut each sandwich into quarters, making rectangles, squares, or triangles. Garnish with parsley sprigs, if desired.
Note: If made ahead, cover sandwiches with a slightly damp paper towel and plastic wrap, and place in an airtight container.
MyRecipes is working with Let's Move!, the Partnership for a Healthier America, and USDA's MyPlate to give anyone looking for healthier options access to a trove of recipes that will help them create healthy, tasty plates. For more information about creating a healthy plate, visit www.choosemyplate.gov.