How can I draw this 2d shape? (two straight lines and two curved segments)

layla over at facepunch.com wrote a script that fully answered my question

Quickly made a script to do this for you. Obviously you don't want to be generating the mesh every frame so just use it to generate it once then draw it however you want.

 using UnityEngine;
 using System.Collections;

 [RequireComponent(typeof(MeshRenderer), typeof(MeshFilter)), ExecuteInEditMode]
 public class CircleMesh : MonoBehaviour
 {
     public int SegmentCount;
     public float OuterRadius;
     public float InnerRadius;
     public float DeltaStart;
     public float DeltaSize;

     private Mesh _mesh;

     private void Awake()
     {
         _mesh = new Mesh();

         GetComponent<MeshFilter>().sharedMesh = _mesh;
     }

     private void Update()
     {
         UpdateMesh();
     }

     private void UpdateMesh()
     {
         _mesh.Clear();

         Vector3[] vertices = new Vector3[(SegmentCount + 1) * 2];
         int[] indices = new int[SegmentCount * 6];

         for (int i = 0; i <= SegmentCount; ++i)
         {
             float angle = (DeltaStart * Mathf.Deg2Rad) + ((DeltaSize * Mathf.Deg2Rad) / SegmentCount) * i;
             Vector2 direction = new Vector2(Mathf.Cos(angle), Mathf.Sin(angle));

             vertices[i * 2] = direction * OuterRadius;
             vertices[(i * 2) + 1] = direction * InnerRadius;
         }

         for (int i = 0; i < SegmentCount; ++i)
         {
             int baseIndex = i * 6;

             indices[baseIndex] = (i * 2);
             indices[baseIndex + 1] = ((i * 2) + 1);
             indices[baseIndex + 2] = (((i + 1) * 2) + 1);

             indices[baseIndex + 3] = (((i + 1) * 2) + 1);
             indices[baseIndex + 4] = ((i + 1) * 2);
             indices[baseIndex + 5] = (i * 2);
         }

         _mesh.vertices = vertices;
         _mesh.triangles = indices;
     }
 }