Do you mean Mt Ventoux in France, frequently part of the the TDF and classed as a real bastard of a climb?
Looking at segments like https://www.strava.com/segments/993229 even the top riders struggle to get 14 km/h I'd be grinding away at 4 to 5 km/h.
From http://www.veloventoux.com/?c=montVentoux where there's analysis of all three approaches.
Any geared bike can climb this, provided you can push the pedals - that is, the only thing that will stop you is running out of leg muscle in your bottom gear.
Since you imply you've done this before, I guess you're asking how to do it better.
Tyre choice - Assuming you're not changing rim size, then you're asking about width and tread. I'd recommend the thinnest tyre that your rims will support. This may be a commuter tyre with a 1.25" width and as smooth a tread as possible. Knobblies are less suitable. Pressure should be at the upper end of the supported range for your tyre.
Descending at speed - I have higher peak and average speeds on my MTB than I get on my road bike. So the wider handlebars of a MTB will give more stability and confidence.
Braking technique helps - you need to corner cleanly and stay well to the correct side of the road. Brake hard on the front with your bum backwards to wash off speed, then lean into the corners, and power on to exit them. Keep the eyes aimed at where you want to go, not the road in front of you. Do not ride the brakes - you'll get better effect from 2 seconds hard brakes on then 2 seconds off than you would from continuous dragging on brakes. You can also sit up and use wind to slow you down a bit. Most of all, don't ride like a prat.
Your bike appears to be a single-sided fork on a rigid MTB diamond frame, maybe with a small damper in the headset. I have no experience with single sided forks, but for the climb you'd want to lock out any suspension, and "lower" it if possible. For the road descent you may want to re-enable the suspension, I've got no experience, so no opinion either way on this.
Also, your single-sided fork.... Again I've never ridden a bike like this, it should be fine, but there are many increased forces at work. I suggest you do some more research on this.
My other suggestion is to not ride the MTB. See if you can hire or rent or borrow a suitable road bike and see how it compares. When I went from a 17KG rigid steel MTB to an 11KG aluminium road bike, my climb times dropped by 15-20%. They didn't feel any faster, so I have to rely on strava to show me my improvements.
Your other technique will be pacing - don't blast up the first climb and run out of herbs, learn your maximum sustainable pace, and methods for keeping to it.