Preheat oven to 350-degree oven F.
Line a baking sheet with parchment paper.
Prepare the cauliflower by removing the outer green leaves and lightly trimming the bottom stem.
Rest the stem side of the cauliflower down on a cutting board. Carefully, slice each head into about 4 thick slices. Place the cauliflower slices onto the prepared parchment-lined baking sheet.
Using an immersion blender or a small food processor, combine the lemon juice, grated Romano cheese, minced garlic, chopped parsley, and 1/3 cup extra-virgin olive oil. Blend to combine well.
Using only about half of the mixture, brush it evenly onto the cauliflower pieces.
Bake in the preheated oven for 30 minutes, remove, brush the cauliflower again, and return to the oven for another 30 - 40 minutes, or until a toothpick inserted into the thickest stem can be inserted easily.
If desired, lightly brush the cauliflower slices with a little extra-virgin olive oil just before serving to add a bit of shine.
Can be served immediately or at room temperature.