Make the filling. In a large skillet over medium high heat, heat the oil.
Add the sausage and cook, breaking the chunks apart with your spatula or spoon, until browned, 1 to 2 minutes per side.
Add the garlic, basil, oregano, fennel seeds, and ground black pepper and cook, stirring, until fragrant, 1 to 2 minutes.
Add the canned tomatoes, tomato paste, vinegar or juice, and sugar and stir to combine. Break the tomatoes into small chunks using a wooden spoon.
Bring to a boil. Reduce the heat to medium low and simmer, stirring occasionally, until most of the liquid has evaporated and sauce has thickened, about 30 minutes.
Add the salt and red pepper flakes. Remove from heat.
In a medium sized bowl, add the cheeses and toss to thoroughly combine.
Stir in the cheese mixture into the sauce.
Spread the filling in a tray and let cool, about 30 minutes. Divide the filling to roughly 16 equal-sized portions.
Make the dough, substituting the cooking oil with olive oil, and adding 1 tablespoon pizza dough flavor (optional) and 1 teaspoon paprika powder to the flour. When the dough is done resting for 10 to 15 minutes, transfer to a lightly dusted surface.
Divide the dough into 16 equal sized pieces.
Prepare 16 pieces of plain paper or reusable silicone baking sheets, about 8cm by 8cm square. Arrange them in your steamer basket, leaving some space in between.
Working with one piece of dough at a time and keeping the rest covered, shape the dough into a ball.
Flatten the dough with the palm of your hand. Using a floured rolling pin, roll the dough into a 1/4-inch thick disc.
Place your rolling pin on about 1/3 of the disc from the top. Roll outwards. Turn the disc about a quarter turn, and repeat. Repeat until you have a disc with a thinner outer ring but still about 1/4 inch thick in the centre.
Scoop a portion of the filling onto the center of the disc. Pleat to seal.
Place on your prepared paper squares in the steamer basket. Repeat for the remaining dough. Let rest, covered, about 45 minutes.
Before steaming the buns, lightly spray them with water. Wrap the lid of your steamer with a large cloth. This will prevent the condensation from dripping onto the buns.
Place the basket over your steamer, cover tightly with the lid and steam, 10 to 15 minutes.
Do not open the lid and let the buns rest undisturbed for about 10 minutes after turning off the heat.