Preheat the oven to 400 degrees F (200 degrees C). Lightly grease a baking sheet.

Bring water to a boil in a medium saucepan. Stir in rice. Reduce heat, cover, and simmer until liquid is absorbed, about 20 minutes. Remove from heat and set aside.

Meanwhile, place peppers cut-side down on the prepared baking sheet. Roast in the preheated oven until tender and skin begins to brown, 25 to 30 minutes.

While peppers are roasting, heat oil in a medium skillet over medium-high heat. Cook and stir onions, basil, Italian seasoning, salt, and pepper in oil for 2 to 3 minutes.

Stir in tomato and cook for 5 minutes. Spoon in cooked rice and stir until heated through.

Remove from heat, mix in feta cheese, and spoon mixture into pepper halves.

Return peppers to the oven until warmed through, about 5 minutes.