Preheat oven to 350 ℉.
Place the sliced Brussels sprouts in a roasting pan. Add the 4 tbsp of olive oil and tsp of salt. Toss thoroughly to coat and spread the sprouts evenly across the pan.
Bake for 25 to 30 minutes, turning occasionally, until the sprouts are tender and slightly browned (you want them to be a little crispy).
While the sprouts are roasting, prepare the herbed dijon. In a small bowl, whisk together the dijon mustard, 3 tbsp of olive oil, rice vinegar, mirin, fresh thyme and fresh oregano. Alternatively, add all dressing ingredients to a jar, cover and shake well.
Once the sprouts are out of the oven, immediately toss them with the herbed dijon dressing. Serve warm.