This requires earning enough gears to unlock all of the mods. You earn gears by completing challenges, but you do not need to get 5 gears in every challenge to earn enough to unlock all mods.
Below is a list of the number of gears required to unlock all mods in each category:
Destruction: 100 (25 challenges available, maximum gears = 125)
Explosives: 45 (12 challenges available, maximum gears = 60)
Weapon: 20 (5 challenges available, maximum gears = 25)
Tether: 15 (4 challenges available, maximum gears = 20)
Traversal: 105 (27 challenges available, maximum gears = 135)
Land Vehicle: 70 (18 challenges available, maximum gears = 90)
Air Vehicle: 40 (12 challenges available, maximum gears = 60)
Sea Vehicle: 35 (9 challenges available, maximum gears = 45)
When you have all mods unlocked, each one needs to have been activated for at least a minute. They don't all have to be active at the same time, so I suggest activating them as you unlock them and then deactivating them after a couple of minutes if you don't want to keep them active.