Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Clean the portobello mushrooms by gently wiping them with a damp cloth. Remove the stems if desired. Brush both sides lightly with olive oil and season with salt, pepper, and half of the fresh herbs.
Place the mushrooms on the baking sheet and roast in the oven for about 15-20 minutes, until tender and slightly crisp at the edges.
While the mushrooms are roasting, prepare the tempeh. Slice the tempeh into 1/4-inch thick steaks. In a small bowl, toss the tempeh slices with a drizzle of olive oil, a pinch of salt, pepper, and a splash of lemon juice. Optionally, sprinkle a bit of the remaining herbs. Grill or pan-sear the tempeh over medium heat for about 3-4 minutes per side until golden and firm.
For the garlic cauliflower mash, cut the cauliflower into florets and steam or boil until very tender, about 10 minutes. Drain well.
In a food processor, combine the cooked cauliflower, garlic, lemon juice, a small drizzle of olive oil, and remaining herbs. Blend until smooth and creamy. Season with salt and pepper to taste.
To serve, place a generous scoop of garlic cauliflower mash on the plate, top with a roasted portobello mushroom cap, and arrange the grilled tempeh steaks alongside. Garnish with a sprinkle of fresh herbs if desired.