Press the tofu. Use a tofu press or weigh it down with heavy objects for at least 30 minutes. Alternatively, wrap the tofu in paper towels and microwave it in 30-second increments for 2 minutes to draw out the excess moisture.
Cut the tofu. Cut the tofu block through the long edge, then into 0.5-inch (1,3 cm) planks or into cubes if cooking the tofu in a pan.
Make the harissa sauce. Mince the garlic with a knife or use a garlic press. Add the olive oil, tomato paste, harissa, minced garlic, oregano, thyme, and salt to a small bowl and combine. Set aside.
To cook it in a pan: Heat a pan over medium-high heat with olive oil. Sear the tofu for 2 minutes per side. Flip the tofu again and reduce the heat to medium-low. Cook for another 5 minutes per side to get a really crispy crust. If using tofu cubes, cook them for 4-5 minutes on each side. Transfer to a plate.
To cook it on the grill: Preheat your grill to 475-500°F (245-260°C). Once hot, clean it with a grill brush to prevent the tofu from sticking. Place the tofu over the burners at medium-high heat. Close the grill and cook the tofu for 2 minutes per side until beautiful grill marks appear. Flip the tofu and move it away from the burners (e.g., on the sides or at the back of the grill) and continue grilling for 5 minutes per side at indirect heat until crispy. Transfer to a plate.
Serve. Brush the harissa mixture onto the tofu planks. Serve with thyme, basil, a squeeze of lemon juice, and lemon zest if desired.
Notes
Spice level: Different brands of harissa paste have different spice levels, so adjust amounts to your liking.