Blanch green beans for about 3-4 minutes in salted, boiling water. Drain and rinse with very cold water, or place them in a bowl of ice water for a few minutes until they are cool. Drain and place green beans into a baking dish.
Spray a non-stick skillet with non-fat cooking spray and set over medium high heat. Cook the bacon pieces for a few minutes, and then add in onion and garlic and continue to cook for another 3-5 minutes, or until the bacon is entirely cooked through and onions begin to become golden brown. Set aside.
In a medium sized sauce pan, melt butter over medium high heat. Add in flour and whisk it into the butter. Let cook for a minute or two, then slowly add in the milk and broth, continuing to constantly whisk. While the sauce thickens, which should take about 5-7 minutes. Then add in the paprika, salt, pepper and cheddar cheese, and stir until cheese is thoroughly melted.
Turn off heat, and add in the pimentos and the bacons/onions, and stir well. Taste, and season with additional salt/pepper as desired.
Pour cheese sauce over the green beans, and gently stir to combine. Top with Panko and place in oven to cook for about 30 minutes, or until sauce is bubbling and Panko becomes golden.