Bring a medium saucepan of salted water to a boil. Add the orzo and cook as the label directs. Reserve 1/4 cup cooking water, then drain. Transfer the orzo to a large bowl and add 2 tablespoons butter, the lemon zest, half of the lemon juice and 2 tablespoons of the reserved pasta cooking water. Season with salt and pepper; toss, adding more pasta cooking water as needed to loosen. Cover to keep warm.
Pat the scallops dry and season with salt and pepper. Heat the olive oil in a large nonstick skillet over medium-high heat. Add the scallops and cook until browned on the bottom, about 3 minutes. Flip and cook until just cooked through, 1 to 2 more minutes. Transfer to a plate; cover to keep warm.
Add the garlic to the skillet. Cook, stirring, until golden, about 10 seconds. Add the wine, 1/4 cup water and the remaining lemon juice. Cook until reduced by half, about 3 minutes. Add the capers and the remaining 3 tablespoons butter; swirl to melt. Stir in the parsley.
Add the arugula and tomatoes to the orzo; toss. Serve with the scallops and pan sauce.