In a large bowl, mix ricotta, 1/2 cup romano cheese, the basil, eggs, olive oil, and 1/2 teaspoon pepper until well blended. Add 2 cups of the semolina and stir until evenly moistened.
Scrape dough onto a board lightly coated with semolina and knead until it forms a smooth ball that's no longer sticky, about 20 turns, adding more semolina as needed to prevent sticking.
Cut dough into 10 pieces. With your fingers, roll each into a 1/2-inch-thick rope. Cut ropes into 1-inch pieces and lay, slightly apart, on baking sheets lightly coated with semolina.
In an 8- to 10-quart pan over high heat, bring 5 quarts water and 1 tablespoon salt to a boil. Gently push gnocchi into water and cook, stirring occasionally, until tender to bite, about 10 minutes. Drain.
Spoon marinara sauce into a bowl and mound gnocchi on top. Add more salt, romano, and pepper to taste.