Set the oven at 425°. Put the bread cubes in the oven while it heats and toast them until golden brown, about 6 minutes.
Twist the wings of the Cornish hens behind their backs and tie the legs together. Put the hens, breast-side up, in a roasting pan. Coat the hens with 1 tablespoon of the oil; sprinkle with 1/4 teaspoon of the salt and 1/8 teaspoon pepper. Dot with the butter. Roast the hens until just done, about 40 minutes.
Meanwhile, oil a deep 1-quart baking dish. In a large bowl, toss the tomatoes with the garlic, parsley, rosemary, the remaining 3/4 teaspoon salt, and 1/4 teaspoon pepper. Add the toasted bread cubes and the remaining 2 tablespoons oil and stir well to combine. Put the stuffing in the prepared baking dish and cover with a lid or with aluminum foil. Bake for 20 minutes. Remove the cover; bake until the stuffing is crisp and golden brown, about 12 minutes longer.
When the hens are done, transfer them to a plate and leave to rest in a warm spot for about 10 minutes. Pour off the fat from the roasting pan and add any accumulated juices from the hens. Cut the hens in half and serve with the stuffing and the pan juices.
Menu Suggestion: Only a green vegetable, perhaps broccoli rabe, is needed to complete the meal.
Wine Recommendation: This rustic, Italian-influenced recipe will go nicely with an Italian red such as a Chianti Classico. It combines fruit flavors with the acidity to stand up to the strong ingredients here.