Toss cauliflower florets with olive oil, salt, pepper, and oregano. Spread on a baking sheet and roast at 400°F (200°C) for 20–25 minutes, or until golden and crisp on the edges.
Rinse the lentils and simmer in salted water until tender but still firm, about 20 minutes. Drain well and let cool slightly.
Make the dressing
In a small bowl, whisk together olive oil, red wine vinegar, lemon juice, Dijon mustard, oregano, basil, salt, and pepper.
Toast the almonds
Add slivered almonds to a dry pan and toast over medium heat for about 3-5 minutes, or until golden and fragrant, stirring often.
Assemble the salad
In a large bowl, mix the cooked lentils, roasted cauliflower, olives, chopped parsley, toasted almonds, and crumbled feta.
Taste and adjust
Drizzle with dressing and toss to combine. Taste and add more salt, lemon juice, or herbs if needed. Serve warm, at room temperature, or chilled.