Preheat oven to 220°C / 425°F. Line a baking sheet with parchment paper.
In a medium saucepan, bring water to a boil. Add jicama and cook until fork tender, about 10 minutes.
Drain water and transfer jicama slices to a large bowl. Toss with olive oil, paprika, onion powder, cayenne powder and salt.
Place jicama slices on the baking sheet. Bake until crispy, turning halfway, about 35-45 minutes.
Slice steak into thin strips. In a large skillet, heat olive oil over medium-high heat. Add beef to skillet and season with salt.
Cook until beef is just golden on the outside or to your desired internal temperature. Remove from skillet. Set aside.
Using the same skillet, add onions and sauté until golden brown. Remove from heat and set aside.
Slice baguette lengthwise, spread mustard on both sides of bread. Follow with slices of steak and Havarti cheese. Keep sandwich open and broil until cheese is bubbly and melted, about 2 minutes.
Serve sandwich warm with jicama fries.