Whisk together the mustard and vinegar in a large bowl. Drizzle in the olive oil, whisking until the dressing is emulsified. Season with 1/4 teaspoon salt.
Using a knife or mandoline, thinly slice the apple into half-moons. Add the apples to the dressing and toss to coat. Add the arugula, smoked almonds and 1/4 teaspoon salt; toss to coat. Dollop the ricotta over the top and serve immediately.
The ricotta cheese can be substituted with goat cheese, feta or any other creamy, crumbly cheese you have on hand.