Put ½-cup panko crumbs in a shallow plate and set aside.
In a mixing bowl combine 1 cup panko crumbs, diced peppers, onions, mayonnaise, egg, old bay seasoning, oregano, thyme, garlic powder, salt, and pepper.
Add the crab meat; mix and stir it all together until thoroughly combined. If mixture is too wet, add more crumbs to reach desired consistency.
Divide the mixture into 8 balls.
Roll each crabmeat ball in the reserved panko crumbs.
Flatten the cakes to make a thick patty.
Heat oil and butter in a large nonstick skillet set over medium-high heat.
Add crab cakes to the hot oil; cook for 3 minutes, or until golden brown.
Flip over the crab cakes and continue to cook for 3 more minutes, or until golden brown.
Transfer crab cakes to a paper towel lined plate to drain.
In the meantime preheat oven to 350˚F.
Line a baking sheet with parchment paper and set aside.
Using a large serrated knife, slice the rolls in half as you would slice a bagel, separating the tops from the bottoms.
Transfer the bottom layer of the buns to the prepared baking sheet, cut side up.
In a bowl combine the mayo and mustard; mix until well incorporated. Set 2 tablespoons aside.
Spread the remaining mayo mixture over the rolls that are on the baking sheet.
Top the rolls with the cooked crab cakes, leaving about ½-inch space between each crab cake. You might not end up using all the crab cakes. I use about 6 crab cakes for the sliders.
Pop in the oven for 10 minutes.
Remove from oven; add baby spinach over each crab cake and add the other half of the rolls on top.
Brush the tops with the reserved mayo mixture.
Put back in the oven for 8 more minutes, or until tops are browned.
Remove from oven and let stand few minutes.
Cut into sliders and serve.