Heat the oil in a heavy medium skillet over medium-low heat. Add the garlic, let it cook for 1 to 2 minutes and then add the herbs and saute until fragrant, about 30 seconds. Cool to room temperature. Whisk in the lemon juice. Season the dressing with salt and pepper, to taste.
Prepare the barbecue (medium-high heat). Pat the scallops and squid dry with paper towels and thread them onto skewers. Brush them with 2 tablespoons of the dressing. Sprinkle with salt and pepper. Grill the scallops and squid until just cooked through, turning once, 2 to 3 minutes per side. Cool completely. Cut the squid crosswise into 1/4-inch-wide rings.
Combine the arugula, carrots, bell peppers, and cannellini beans in a large bowl. Toss with 1/2 cup of the dressing to coat.
Place 1 large or 2 medium radicchio leaves on each of 4 plates. Spoon the bean salad into the radicchio cups. Top with the scallops and squid. Drizzle the remaining dressing over the seafood and serve.