Preheat oven to 400°F.
Toss together tomatoes, shallots, garlic, oregano, salt, black pepper, crushed red pepper, and 4 tablespoons oil in a 13- x 9-inch baking dish.
Place feta in center of baking dish, and drizzle feta with remaining 2 tablespoons oil.
Bake until tomatoes are blistered and sauce is bubbling, about 35 minutes.
Meanwhile, bring a large pot of salted water to a boil over high.
Add pasta, and cook according to package directions, 10 to 15 minutes.
Reserve ½ cup cooking liquid; drain pasta, and set aside.
Remove baking dish from oven.
Mash and stir feta with tomatoes and their juices, creating a sauce.
Stir in pasta and harissa until well combined.
Add reserved cooking water, 2 tablespoons at a time, until desired consistency is reached.
Garnish with basil and additional black pepper.
Serve immediately.
